Spontaneous circadian rhythms in a cold-adapted natural isolate of Aureobasidium pullulans

Diana L Franco,Diego Libkind,Nicolás Bellora,Sebastián Risau-Gusman,Consuelo Olivares-Yañez,Luciano Marpegan,Paulo Canessa,Rodrigo Pérez-Lara,Luis F Larrondo

doi:10.1038/s41598-017-14085-6

Abstract

Circadian systems enable organisms to synchronize their physiology to daily and seasonal environmental changes relying on endogenous pacemakers that oscillate with a period close to 24 h even in the absence of external timing cues. The oscillations are achieved by intracellular transcriptional/translational feedback loops thoroughly characterized for many organisms, but still little is known about the presence and characteristics of circadian clocks in fungi other than Neurospora crassa. We sought to characterize the circadian system of a natural isolate of Aureobasidium pullulans, a cold-adapted yeast bearing great biotechnological potential. A. pullulans formed daily concentric rings that were synchronized by light/dark cycles and were also formed in constant darkness with a period of 24.5 h. Moreover, these rhythms were temperature compensated, as evidenced by experiments conducted at temperatures as low as 10 °C. Finally, the expression of clock-essential genes, frequency, white collar-1, white collar-2 and vivid was confirmed. In summary, our results indicate the existence of a functional circadian clock in A. pullulans, capable of sustaining rhythms at very low temperatures and, based on the presence of conserved clock-gene homologues, suggest a molecular and functional relationship to well-described circadian systems.

Highlights

Circadian systems are ubiquitous, they are present in organisms ranging from bacteria to humans, including plants, insects and fungi[1], enabling synchronization of key biochemical, cellular and physiological processes to cyclic environmental events
The study of the core molecular oscillator in N. crassa revealed that the transcription factor/photoreceptor White Collar-1 (WC-1) associates with its partner White-Collar-2 (WC-2) forming the White Collar Complex (WCC), a positive element that activates the expression of the negative element: the frequency gene
These results show that the ring pattern is temperature compensated, a characteristic feature of processes under circadian control. To our knowledge this is the first evidence of a fungal rhythmic phenotype reported at such low temperatures. These results suggest that concentric ring formation in A. pullulans is a circadian phenotype controlled by an endogenous, temperature compensated oscillator that can be entrained to 24 h light/dark cycles

Summary

Introduction

They are present in organisms ranging from bacteria to humans, including plants, insects and fungi[1], enabling synchronization of key biochemical, cellular and physiological processes to cyclic environmental events (mostly to daily and seasonal variations). These molecular oscillations are regulated at the transcriptional level and at the post-translational level, by changes in the phosphorylation status of the negative elements controlling protein stability, activity, dimerization and subcellular localizations[11] Because of their ecological and economical properties fungi are critical for humans and the environment. Most of what is known about fungal circadian systems derives from experiments on N. crassa, but our knowledge on the circadian properties and the underlying molecular and cellular mechanisms of the vast majority of fungi remains extremely limited

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